Field of the Invention
The invention lies in the field of internal combustion engine technology. More specifically, the invention relates to a method for controlling an internal combustion engine as a function of an exhaust gas pressure, in particular an internal combustion engine which has servo-drives for setting the load on the internal combustion engine, which act on the gas exchange valves of the cylinders of the internal combustion engine.
Commonly assigned U.S. Pat. No. 5,974,870 (see international PCT publication WO 97/35106) discloses a method for controlling an internal combustion engine in the case of which an intake pipe pressure and a gas mass flow into a cylinder of the internal combustion engine are determined. A dynamic model is provided for this purpose of the intake tract of the internal combustion engine and of an external exhaust gas recirculation via a pipe which is guided away from an exhaust gas tract to the intake tract of the internal combustion engine and in which an exhaust gas recirculation valve is arranged. The dynamic model is derived from equations for the mass flow balances in the intake tract and from the flow equations of ideal gases at throttle points. The measured variables of speed and degree of opening of the throttle valve are input variables of the dynamic model. An exhaust gas pressure in the exhaust gas tract is also determined for the purpose of calculating the mass flow at the exhaust gas recirculation valve. This is performed by using a characteristic diagram for parameterization as a function of operating point, or by evaluating the signals of appropriate sensors.
The object of the present invention is to provide a method of controlling an internal combustion engine which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which is precise and simple even in the case of internal exhaust gas recirculation.
With the above and other objects in view there is provided, in accordance with the invention, a method of controlling an internal combustion engine in dependence on an exhaust gas pressure, the internal combustion engine including an intake tract, at least one cylinder, an exhaust gas tract, inlet and outlet valves disposed at the cylinder and driven, in particular, with electromechanical servo-drives. The method comprises the following steps:
determining an exhaust gas pressure in the cylinder during a valve overlap of the inlet and outlet valves that causes an internal exhaust gas recirculation in dependence on
an estimated value of an exhaust gas pressure effected by a combustion of an air/fuel mixture in the cylinder, and
a variable characterizing a centroid of the valve overlap of the inlet and outlet valves, and thereby defining the centroid with reference to a surface produced by the overlapping valve strokes of the inlet and outlet valves referred to a crankshaft angle.
The valve overlap is the range of the crankshaft angle in which both the inlet valve and the outlet valve expose at least a part of their flow cross sections at the inlet and outlet ports of the cylinder. At least one actuating signal for controlling an actuator of the internal combustion engine is derived from an exhaust gas pressure, or the internal combustion engine is monitored as a function of the exhaust gas pressure.
In accordance with an added feature of the invention, the estimated value of the exhaust gas pressure effected by the combustion of the air/fuel mixture in the cylinder depends on a gas mass flow into the cylinder.
In accordance with an additional feature of the invention, the variable characterizing the centroid of the valve overlap of the inlet and outlet valves is a center of gravity angle of the centroid of the valve overlap referred to the crankshaft angle.
In accordance with another feature of the invention, the center of gravity angle is a function of a closing angle of the outlet valve, of an angle segment of the valve overlap and of a prescribed correction value.
In accordance with a further feature of the invention, the correction value is defined in dependence on a variable influencing a closing rate or an opening rate of the inlet or outlet valves.
In accordance with again an added feature of the invention, a mass flow resulting from internal exhaust gas recirculation is determined as a function of the exhaust gas pressure and an intake pipe pressure in the intake tract.
In accordance with again an additional feature of the invention, the mass flow resulting from internal exhaust gas recirculation is determined as a function of a mean flow cross section at the inlet valve of the cylinder during the valve overlap.
In accordance with again another feature of the invention, the mean flow cross section is a function of the angle segment of the valve overlap.
In accordance with again a further feature of the invention, the mass flow into the cylinder is determined with a dynamic model of the internal combustion engine as a function of the mass flow resulting from internal exhaust gas recirculation, and of at least the measured variables of the degree of opening of a throttle valve in the intake tract and of a speed of the crankshaft.
In accordance with a concomitant feature of the invention, the exhaust gas pressure depends on an ambient pressure.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for controlling an internal combustion engine as a function of an exhaust gas pressure, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.